1. Field of the Invention
This invention relates to methods for compression and expansion of digital audio data having small latency.
This application claims priority on Japanese Patent Application No. 2005-159484, the content of which is incorporated herein by reference.
2. Description of the Related Art
It is well known that methods for compressing digital audio data are realized by way of ADPCM (i.e., Adaptive Differential Pulse-Code Modulation) and LPC (i.e., Linear Predictive Coding) as well as sub-band coding such as MP3 (i.e., MPEG Audio Layer 3) and MPEG Audio AAC (Advanced Audio Coding).
Linear predictive coding methods perform compression on digital audio data in units of samples so that they can start playback (or tone-generation processing) without delays due to expansion (or decoding); hence, they realize small tone-generation latency but not realize a high compression ratio in comparison with sub-band coding methods. Sub-band coding methods perform compression on plural samples in units of frames (or blocks); hence, they realize a high compression ratio in comparison with linear predictive coding methods. However, sub-band coding methods cannot start playback before completion of expansion of all samples included in a top frame; hence, an expansion time becomes longer as the number of samples included in each frame becomes large, which in turn increases tone-generation latency. Documents entitled Japanese Patent No. 2734323 and International Publication No. WO99/29133 teach data compression methods realizing improvements of tone-generation latencies while securing high compression performance.